1. Field of the Invention
The invention relates generally to underground storage tanks and more particularly to the installation of street boxes for underground storage tanks including risers, especially double walled risers.
2. Discussion of the Background
Underground storage tanks are used in a wide variety of locations to store liquid materials underground. The stored materials are often harmful to the environment. Examples of such materials include gasoline and other petroleum products, e.g., oil and waste oil, as well as toxic raw materials and waste from manufacturing processes. Because of the harmful nature of these materials, it is especially important to ensure that underground storage tanks containing such materials do not leak or release these materials into the environment.
Concern over this possibility has lead many governmental authorities to require secondary containment for tanks that store such materials. One of the most common methods for providing secondary containment is through the use of multiple-walled underground storage tanks. The assignee of the present application, Xerxes Corporation, has manufactured and sold double walled underground storage tanks prepared from corrosion resistant materials such as fiber reinforced plastic (FRP) since 1984. These tanks have proven very reliable.
Underground storage tanks with manways often include risers. A riser is typically tubular, surrounds the manway, and extends from the manway upward to a point just beneath ground level. Risers often come equipped with covers. An example of a watertight riser cover is described in U.S. Pat. No. 5,595,496, owned by the assignee of the present application. Flex connectors or other devices in fluid communication with the interior of the tank sometimes pass through the wall of the riser and the manway covers. In such instances, it is known in the art for the riser to act as a containment sump to contain any leaks that occur at the joints between such devices and the manway cover and/or the joints between such devices and the riser wall.
A device known as a “street box” is often placed over the top of the riser and riser cover (if a riser cover is provided) to provide for access to the riser from ground level. A street box typically includes a 1″ steel cover and a “box” that has a recessed lip for receiving the lid. The box can be any shape, but is often circular with a diameter larger than that of the riser.
In many installations, especially gasoline filling stations, the street box is subject to being driven over by cars and trucks. It is important to prevent the weight of these vehicles from being transferred to the riser. Therefore, street boxes in such situations are often set in concrete to distribute the force exerted on the street box by cars and trucks over a wide area.
Recently, concern for leaks has led the state of California to mandate secondary containment for such riser containment sumps. The assignee of the present application, Xerxes Corporation, has invented a double walled riser to meet this requirement for secondary containment as described in co-pending U.S. patent application Ser. No. 10/796,198, filed Mar. 10, 2004 and entitled “Double-Wall Containment Sumps”, the entire contents of which are hereby incorporated by reference herein.
More recent California regulations include a requirement that there be a barrier between the riser sump and the backfill surrounding the riser from the point in the riser at which the double-wall containment ends (in the preferred embodiment of the aforementioned double wall riser application, this is a point near the top of the vertical wall of the riser) and ground level. The aforementioned concrete pad can serve this purpose if the depth of the concrete extends below the point in the riser sidewall at which the double containment ends. However, with known installation methods, meeting this requirement and verifying that this requirement has been complied with can be troublesome. What is needed are methods and devices that facilitate compliance and verification of compliance with the new California requirement.